Intrinsic and extrinsic factors involved in regulation of sperm motility contribute to the wide range of swimming speeds and patterns of movement exhibited by the individual sperm cells contained in the population of even a single semen sample. The sperm cell responds to such stimuli as physical and chemical changes in its environmental milieu via receptor-transmitter mechanisms which appear to be located at, on or in the cell membrane. Cholinomimetic as well as anti-cholinergic agents exert concentration- and time-dependent effects on the rate of motility and swimming pattern and one or more of the flagellar wave parameters, viz, frequency, amplitude, propagation rate and occasionally direction. We are studying enzyme distribution and reactin kinetics cytochemically and biochemically, as well as measuring membrane potential by intracellular microelectrode as affected by a variety of ions and pharmacologic agents. We are also determining how these chemical factors, as well as temperature and viscosity influence the swimming rate and fertilizing capacity of the treated cells.